161 research outputs found
Excitations in disordered bosonic optical lattices
Spectral excitations of ultracold gases of bosonic atoms trapped in one
dimensional optical lattices with disorder are investigated by means of the
variational cluster approach applied to the Bose-Hubbard model. In particular,
qualitatively different disorder distributions typically employed in
experiments are considered. The computed spectra exhibit a strong dependence on
both the shape of the disorder distribution and the disorder strength. We
compare alternative results for the Mott gap obtained from its formal
definition and from the minimum peak distance, which is the quantity available
from experiments.Comment: 8 pages, 7 figures, version as publishe
Competition Between Charge-Density Waves and Superconductivity in Striped Systems
Switching on interchain coupling in a system of one-dimensional strongly
interacting chains often leads to an ordered state. Quite generally, there is a
competition between an insulating charge-density-wave and a superconducting
state. In the case of repulsive interactions, charge-density wave usually wins
over superconductivity. Here, we show that a suitable modulation in the form of
a period 4 bond-centered stripe can reverse this balance even in the repulsive
case and produce a superconducting state with relatively high temperature.Comment: Proceedings of SCES 04, 2 page
Time-reversal symmetry breaking phase in the Hubbard model: a VCA study
We study the stability of the time-reversal symmetry breaking staggered flux
phase of a single band Hubbard model, within the Variational Cluster Approach
(VCA). For intermediate and small values of the interaction , we find
metastable solutions for the staggered flux phase, with a maximum current per
bond at . However, allowing for antiferromagnetic and
superconducting long-range order it turns out that in the region at and close
to half filling the antiferromagnetic phase is the most favorable
energetically. The effect of nearest-neighbour interaction is also considered.
Our results show that a negative nearest-neighbour interaction and finite
doping favors the stability of the staggered-flux phase. We also present
preliminary results for the three-band Hubbard model obtained with a restricted
set of variational parameters. For this case, no spontaneous time-reversal
symmetry breaking phase is found in our calculations.Comment: 9 pages,8 figure
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